Polymers are increasingly used in radiation environments encountered in space crafts, rockets, satellites, airplanes (at high altitude), nuclear power plants, sterilization devices, high energy particle accelerators and other radiation prone environments. However, he use of polymeric materials in primary structures of spacecraft and aircraft is limited by the high temperatures encountered during launch, e.g. combustion gases, aerodynamic heating, and thermal cycling from approximately −175 to 160° C. as a result of exposure to thermal radiation from the sun as well as high-energy ionizing radiations and charging (electrostatic discharge effects). In terms of polymer degradation in space, low Earth orbit, defined as 200-1000 km above the Earth's surface, is a particularly challenging environment, since atomic oxygen is also present.
Ultraviolet light, x-rays, and gamma rays as well as high energy electrons and ions are all ionizing radiation. Ionizing radiation is a portion of the electromagnetic spectrum or type of particle which (for example, a photon, electron, or helium nucleus) carries enough energy to ionize an atom or molecule (that is, to completely remove an electron from its orbit). Galactic cosmic rays are high energy charged particles, originating in outer space and include high energy electrons, positrons, and other subatomic particles. The energy of cosmic rays is usually measured in units of mega-electron volts (MeV) or giga-electron volts (GeV) and have energies between 100 MeV and 10 GeV. Gamma rays may come from space or be produced by decaying radioactive materials. Gamma rays have great penetrating power but less ionizing power and are useful in the sterilizing of medical equipment by killing bacteria. They are also used to kill bacteria in foodstuffs, particularly meat and vegetables, High energy particle accelerators which generate energetic electrons and ions and nuclear devices and reactors which generate Gammas rays and energetic electrons are devices which are used to produce, as defined here, artificial or man-made high energy ionizing radiation. For the purpose of this document high energy ionizing radiation, whether of Galactic or artificial origin, is defined as ionizing radiation having energy above about 20 KeV.